List
The Python List is one of the most useful sequence in real-time. A list is a sequence of multiple values in an ordered sequence. Unlike Python Strings, List allow us to store different types of data such as integer, float, string etc.
List_Name = [] is an empty list that contains no values.
Integer_List = [1, 2, 3, 4, 5] is an integer list that contains five integer values.
String_List = [‘apple’, ‘Orange’, ‘Grape’, ‘Mango’] is a string list that contains four string values.
Mixed_List = [‘apple’, 2, 3.50, ‘Mango’] is a mixed list that contains one integer, one float and two integer values.
Accessing Python List items
We can access the elements in a Python List using indexes. Using index we can access or alter/change each and every individual item present in the Lists separately. Index value starts at 0 and end at n-1 where n is the list size. For example, if a list stores 5 elements then index starts at 0 and ends with 4. To access or alter 1st value use list_name[0] and to access or alter 5th value then use list_name[4]. Lets see the example for better understanding:
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x = [1, 2, 3, 4, 5, 6, 7, 8, 9] # Positive Indexing print(x[0]) print(x[4]) print(x[8]) print('=======\n') # Negative Indexing print(x[-2]) print(x[-4]) print(x[-8]) |
TIP: If you are using the Negative numbers as index then, Python will start looking for items from right to left
OUTPUT
Iterating Python List
The Python For Loop is the most common way to traverse the items in a list. Following statements will help us to iterate the list and print the items inside the list.
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Fruits = ['Apple', 'Orange', 'Grape', 'Banana'] for Fruit in Fruits: print(Fruit) |
Above specified code will work fine to print items inside the list but, In order to alter the individual item we need the index position. To resolve this, we have to use the range function along with for loop as shown below
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# Altering Python List using range x = [1, 2, 3, 4, 5, 6, 7, 8, 9] for Number in range(len(x)): x[Number] = x[Number] * 10 print(x) |
Above specified code will multiply each and every item with 10. If you want to perform the calculation based on condition then, you can use Python If Statement inside the for loop
OUTPUT
Inserting items into Python List
Python provides the following options to insert new items into the existing list
- Append(x): This method will help us to add item x at the end of the list.
- Insert(i, x): This method will help us to insert the specified item x at index position i
- Extend(New_List): This method will help us to add all the items in New_List at the end of the list
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Fruits = ['Apple', 'Orange', 'Grape', 'Banana'] # Adding items using Python append Fruits.append('Blackberry') print(Fruits) # inserting items using Python insert Fruits.insert(2, 'Kiwi') print(Fruits) # Extending List using Python extend Fruit_new = ['Strawberry','Cherry'] Fruits.extend(Fruit_new) print(Fruits) |
OUTPUT
Performing Arithmetic Operations on Python List
In this example we will show you, How to use Python Arithmetic Operators on Lists to perform arithmetic Operations
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X = [1, 2, 3] Y = [4, 5, 6] Sum = X + Y print(Sum) # Using * Operator Z = X * 3 print(Z) |
OUTPUT
From the above screenshot you can observe that,
- + operator is concatenating the python Lists
- * operator is repeating the list for given number of times. Here it is three times
Python List Slicing
In python Slice, the first integer value is the index position where the slicing will start and the second integer value is the index position where the slicing will end.
TIP: Slicing will go up to second integer value but will not include the value at this index position. For instance, if we specify list[1:4] then slicing will start at index position 1 and ends at index position 3 (not 4).
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x = [1, 2, 3, 4, 5, 6, 7, 8, 9] # Slicing the List using two indexes a = x[2:6] print("Both Indexes = ", a) # Slicing the List using First indexes b = x[:6] print("No First Index = ", b) # Slicing the List using Second indexes c = x[2:] print("No Second Index = ", c) # Slicing the List without using two indexes d = x[:] print("No Indexes = ", d) # Slicing the List using Negative indexes e = x[-3:] print("Negative First Index = ", e) # Slicing the List using Negative indexes f = x[:-2] print("Negative Second Index = ", f) # Assigning new values to the List x[1:3] = ['t','g'] print("After altering = ", x) |
OUTPUT
From the above screenshot you can observe that,
- If you omit the first index then, Slicing will start from the beginning
- If you omit the second index then, Slicing will start from the first index and continue to the last
- If you are using the Negative numbers as index then, Slicing starts from right to left
Removing Python List items
There are several ways to delete items from Python Lists:
Removing Python List items using remove() method
If we know the List item or the value inside the List then, we can use python remove() method to remove the list item.
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# Removing Grape Item from Fruit List Fruit1 = ['Apple', 'Orange', 'Grape', 'Banana'] Fruit1.remove('Grape') print(Fruit1) print('========\n') # Removing Orange Item from Fruits List Fruit2 = ['Apple', 'Orange', 'Grape', 'Banana', 'Orange'] Fruit2.remove('Orange') print(Fruit2) print('========\n') # Removing Non Existing Grape Item from Fruits1 List Fruit3 = ['Apple', 'Orange', 'Banana'] Fruit3.remove('Grape') print(Fruit3) |
OUTPUT
From the above screenshot you can observe that,
- Within the First set of statements, We are removing the Grape item from the Fruit1 and displaying the remaining list.
- Within the Second set of statements, We are removing the Orange item from the Fruit2 and displaying the remaining list. If you observe closely, we have two Orange items in this list but remove() method removed only one item. This is because, remove() method will only remove the first instance of the item and ignores the remaining
- Within the Third set of statements, We are removing the non existing item. That’s why it is throwing an error saying x is not in list
Removing Python List items using del statement
The Delete statement will remove the value at specified index and after deleting, remaining values will be moved up to fill the index gap. If we know the Index value or you want to delete range of items from the given List then, we can use python del statement to remove the list item.
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# Delete Statement example in Python List Fruits = ['Apple', 'Orange', 'Grape', 'Banana'] del Fruits[1] print(Fruits) print('========\n') del Fruits[1] print(Fruits) print('========\n') del Fruits[1] print(Fruits) print('========\n') del Fruits[1] print(Fruits) |
OUTPUT
From the above screenshot you can observe that,
- Within the First set of statements, We are deleting the item at index position 1, which is Orange and displaying the remaining list. If you observe closely, after deleting the Orange, the index position of Grape become 1 and Banana as 2
- Within the Second set of statements, We are deleting the item at index position 1, which is Grape and displaying the remaining list.
- Within the Fourth set of statements, We are removing the non existing item. That’s why it is throwing an error saying index out of range
Removing Python List items using pop() method
The pop() method will remove the value at specified index and display the removed element. After removing, remaining values will be moved up to fill the index gap. If we know the Index value and want to see the deleted value then, we can use python pop() to remove the list item.
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# Pop Method example in Python List Fruits = ['Apple', 'Orange', 'Grape', 'Banana'] Fruit = Fruits.pop(1) print(Fruits) print('Item extracted by Python Pop = ', Fruit) print('========\n') Fruit = Fruits.pop(1) print(Fruits) print('Item extracted by Python Pop = ', Fruit) print('========\n') Fruit = Fruits.pop(1) print(Fruits) print('Item extracted by Python Pop = ', Fruit) print('========\n') |
OUTPUT
Python List Methods
Python provides following methods to perform on Lists:
- Copy(): This method will help us to shallow copy the list items
- Clear(): This method will help us to clear all the list items
- Sort(): This method will help us to sort the items in Ascending order
- Reverse(): This method will help us to reverse the list items
- Index(x): This method will help us to return the index position of a specified value
- Count(x): This method will help us to count, How many times the specified value is repeated inside the list
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Fruits = ['Apple', 'Orange', 'Banana', 'Kiwi', 'Grape', 'Blackberry'] x = [9, 4, -5, 0, 22, -1, 2, 14] #Copying the List using Python Copy() Method New_Fruits = Fruits.copy() print(New_Fruits) #Removing all the List items using Python Clear() Method New_Fruits.clear() print(New_Fruits) # Sorting the List using Python Sort() Method Fruits.sort() x.sort() print(Fruits) print(x) # Reverse the List using Python reverse() Method Fruits.reverse() x.reverse() print(Fruits) print(x) # Index position of an item in the List using Python index() Method print('The Index position of Banana = ', Fruits.index('Banana')) print('The Index position of -1 = ', x.index(-1)) # Counting items in the List using Python count() Method y = [9, 4, 1, 4, 9, -1, 2, 4] print('Number of Times 4 is repeated = ', y.count(4)) print('Number of Times 9 is repeated = ', y.count(9)) |
OUTPUT
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